Process for inhibiting edge peeling of coating on semiconductor substrate during formation of integrated circuit structure thereon

ABSTRACT

A photoresist-free and ARC-free lip on the periphery of the upper surface of a semiconductor substrate adjacent the end edge of the substrate is formed by the steps of: forming an ARC layer on one surface of a semiconductor substrate; chemically treating the ARC layer to chemically terminate the ARC layer a first distance from the end edge of the substrate; forming a photoresist layer over the semiconductor substrate and over the ARC layer thereon; and exposing the peripheral portion of the photoresist layer to UV light followed by development of the exposed peripheral portion of the photoresist layer to photolithographically terminate the photoresist layer a second distance from the end edge of the substrate wherein the second distance is smaller than the first distance.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the formation of integrated circuitstructures. More particularly, this invention relates to inhibition ofpeeling and resultant particle and/or flake formation at the edge of asemiconductor substrate during formation of a integrated circuitstructure thereon.

2. Description of the Related Art

In the formation of integrated circuit structures, multiple layers ofelectronic structure are formed, including at least one layer of activedevices and a plurality of metal interconnect layers. Most, if not all,of the layers involve some sort of patterning using photolithographywherein a layer of photoresist is blanket deposit over the surface ofthe semiconductor substrate, then exposed to a pattern of light througha reticle, and the exposed portions of the photoresist are removed by adeveloper solution (when positive resist is used), leaving, in thephotoresist layer, an exact replica of the pattern in the reticle.

While such photolithography is in widespread use, it was recognized manyyears ago that the blanket deposition of photoresist on the uppersurface of the substrate, e.g., by spin-on of the photoresist film,resulted in the undesirable formation of particles or flakes when theend edge of the substrate was grasped either manually or by mechanicalmeans during further steps such as metal deposition processes/thermalcycles, either to move the substrate or to secure it during processing.

This problem of particle/flake formation was addressed in Allen U.S.Pat. No. 4,518,678 which proposed to form a photoresist-free lip on theupper surface of the substrate adjacent the end edge of the substrate bydirecting a stream of a solvent for the photoresist against the end edgeof the substrate.

It was also recognized in the prior art that in the practice ofphotolithography, one could not tolerate exposure of the photoresist toa reflected beam of the pattern of light from the reticle since thereflected light usually was reflected back into the photoresist at anoblique angle rather than at 180°, thus destroying the sharpness of thelight image formed in the photoresist.

This resulted in the practice of providing an antireflective surfacedirectly beneath the photoresist layer to prevent reflection backthrough the photoresist of the pattern of light originally projectedonto the photoresist layer from the reticle.

Since such an antireflective surface was almost always desirablewhenever a resist layer was used, opaque coatings became commerciallyavailable which, although not photosensitive, were removable by liquidsolvents just as the light exposed portions of the photoresist (althoughthe same solvent is not used for both).

Also since the antireflective coating layer (ARC layer), or bottomantireflective coating layer (BARC layer) is the layer beneath thephotoresist layer, and it was considered desirable to have the ARC orBARC layer beneath all of the photoresist layer, it became the practiceto spin on the ARC/BARC layer to the end edge of the semiconductorsubstrate and then to remove the portion of the ARC layer adjacent theend edge of the substrate by directing a flow of solvent against the endedge of the ARC layer, i.e., to remove the portion of the ARC layeradjacent the end edge of the substrate by chemical means just as hadbeen previously done with the photoresist layer.

It then became the custom to spin on the photoresist layer over the ARClayer and to expose the outer edge of the photoresist layer to radiationfollowed by development of the photoresist, resulting in the prior artstructure shown in FIG. 1 wherein an ARC layer 10 is formed over asemiconductor substrate or wafer 2, with the edge 14 of ARC layer 10terminating adjacent end edge 4 of substrate 2; and a photoresist layer20 formed over ARC layer 10, with an outer edge 24 of photoresist layer20 terminating a greater distance from end edge 4 of substrate 2.

However, as the sizes of integrated circuit structures continued toshrink and tolerances became smaller and smaller, it became apparentthat the unevenness of edge 14 of ARC layer 10, as shown magnified at 16in FIG. 2, resulting from the solvent spray directed toward the end edgeof the substrate, was not satisfactory since particle/flake formationstill occurred when wide portions of the resulting uneven edge 16 of ARClayer 10 came into contact with substrate-engaging structures.

SUMMARY OF THE INVENTION

In accord with the invention, a photoresist-free and ARC-free lip on theperiphery of the upper surface of a semiconductor substrate adjacent theend edge of the substrate is formed by the steps of:

a) forming an ARC layer on one surface of a semiconductor substrate;

b) chemically treating the ARC layer to chemically terminate the ARClayer a first distance from the end edge of the substrate;

c) forming a photoresist layer over the semiconductor substrate and overthe ARC layer thereon; and

d) exposing the peripheral portion of the photoresist layer to radiationfollowed by development of the exposed peripheral portion of thephotoresist layer to photolithographically terminate the photoresistlayer a second distance from the end edge of the substrate wherein thesecond distance is smaller than the first distance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary vertical cross-sectional view of a prior artstructure showing chemical termination of an antireflective coating(ARC) layer adjacent the end edge of a substrate with a photoresistlayer shown terminating a larger distance from the end edge of thesubstrate.

FIG. 2 is an enlarged fragmentary vertical cross-sectional view of aportion of FIG. 1 showing the ragged edge of the chemically terminatedARC layer on the substrate.

FIG. 3 is a fragmentary vertical cross-sectional view of a substratewith an ARC layer spun onto the upper surface of the substrate.

FIG. 4 is a fragmentary vertical cross-sectional view of the structureof FIG. 3 showing chemical termination of the ARC layer a first distancefrom the end edge of the substrate.

FIG. 5 is a fragmentary vertical cross-sectional view of the structureof FIG. 4 showing a photoresist layer spun over the upper surface of thesubstrate and over the ARC layer.

FIG. 6 is a fragmentary vertical cross-sectional view of the structureof FIG. 5 showing the photoresist layer photolithographically terminateda second distance from the end edge of the substrate which is smallerthan the first distance.

DETAILED DESCRIPTION OF THE INVENTION

The invention comprises a process for forming a photoresist-free andARC-free lip on the periphery of the upper surface of a semiconductorsubstrate adjacent the end edge of the substrate by the steps of:

a) forming an ARC layer on one surface of a semiconductor substrate;

b) chemically treating the ARC layer to chemically terminate the ARClayer a first distance from the end edge of the substrate;

c) forming a photoresist layer over the semiconductor substrate and overthe ARC layer thereon; and

d) exposing the peripheral portion of the photoresist layer to radiationfollowed by development of the exposed peripheral portion of thephotoresist layer to photolithographically terminate the photoresistlayer a second distance from the end edge of the substrate wherein thesecond distance is smaller than the first distance.

The process of the invention is useful for any photolithographic processusing an antireflective coating and a photoresist layer for theformation of integrated circuit structures including, but not limitedto, patterning of metal or polysilicon for the formation of lines, viaand contact openings, islands, and for implanting.

As illustrated in FIG. 6, the term “end edge of the substrate” andsimilar expressions are intended to define any point at the circularedge of the substrate at which a line at a tangent with the circularedge of the substrate is perpendicular to a line lying in the plane ofthe substrate.

Turning to FIG. 3, a fragmentary portion of a semiconductor substrate 2is shown having spun over its upper surface 6 thereof an antireflectivecoating (ARC) layer 30. Such ARC coating materials are commerciallyavailable, for example, from the Brewer Science Company under thetrademark DUV 44. In accordance with the invention a stream of solventfor ARC layer 30 is directed toward the periphery of ARC layer 30 onfront surface 6 of substrate 2, as generally shown pictorially at 38 inFIG. 3. Apparatus (tools) equipped to provide such a spray through anadjustable nozzle is commercially available, for example, from theTEL/DNS Company under the trademarks ACT-8, 80B, 200W.

The result is the chemically formed edge 36 of ARC layer 30 of FIG. 4which, it will be noted, is terminated a larger distance from end edge 4of substrate 2 than edge 14 of prior art ARC layer 10 of FIG. 1.Although chemically formed edge 36 of ARC layer 30 is shown as a smoothsurface in FIG. 4, it will be appreciated that since ARC layer 30 waschemically terminated, the surface of edge 36 will be uneven, similar tosurface 16 of layer 10 shown in prior art FIG. 2. However, as will bedescribed below, unlike the process of the prior art, formation ofuneven side edge 36 on ARC layer 30, by use of chemical termination ofARC layer 30 does not increase the likelihood of particle or flakeformation during subsequent processing of substrate 2.

In accordance with the invention, a photoresist layer 40 is then spunover upper surface 6 of substrate 2, completely covering ARC layer 30,as shown in FIG. 5. The peripheral portion of photoresist layer 40 isthen photolithographically terminated and removed by exposing theperipheral portion of photoresist layer 40 to a radiation pattern whichexposes only this peripheral portion of photoresist layer 40 to suchradiation, followed by development of such exposed portion ofphotoresist layer 40. Since edge 46, unlike edge 36, isphotolithographically formed, the result is a precise, accurate, andsmooth surface comprising edge 46, thus avoiding the problems of theprior art with respect to particle/flake formation. Apparatus or toolswhich permit such accurate photolithographic patterning of theperipheral portion of photoresist layer 40 is commercially availablefrom the TEL/DNS Company under the trademarks ACT-8, 80B, 200W.

Relative Distances of A and B from End Edge of Substrate

As seen in FIG. 6, the peripheral portion of photoresist layer 40 isterminated photolithographically to form an end edge 46 closer to endedge 6 of substrate 2 than end 36 of chemically terminated ARC layer 30so that the rough edge surface of end edge 36 of chemically terminatedARC layer 30 is completely covered by photoresist layer 40. FIG. 6 showsthat the distance A from end edge point 4 on substrate 2 to thechemically formed end 36 of ARC layer 30 exceeds distance B from endedge 4 of substrate 2 to photolithographically formed edge 46 ofphotoresist layer 40 by an amount A minus B.

Maximum Distance of A

Since stepper apparatus used to subsequently process photoresist layer40 photolithographically does so to within 3 millimeters (mm) of endedge 4 of substrate 2, it is important that the maximum value of A beless than 3 mm (to ensure that there is an antireflective surfacebeneath any portions of photoresist layer 40 exposed to radiation fromthe stepper apparatus). Thus, for example, when substrate 2 is a 200 mmdiameter semiconductor wafer, the minimum diameter of ARC layer 30thereon (after chemical formation of edge 36) should be greater than 194mm, i.e., a minimum radius of ARC layer of greater than 97 mm.

Maximum Distance of B

Furthermore, to ensure that there is sufficient distance between edge 46of photoresist layer 40 and edge 36 of ARC layer 30 to permit formationof the desired accurate photolithographically-formed edge 46 onphotoresist layer 40, the maximum value of B should be at least about0.5 mm less than A. That is, A minus B should equal at least 0.5 mm.Therefore, for the above 200 mm semiconductor wafer, the diameter ofphotoresist layer 40 thereon (after photolithographical formation ofedge 46) should be greater than 195 mm, i.e., a radius of greater than97.5 mm.

Minimum Distances of A and B

However, to permit adequate area for peripheral grasping of substrate 2without risking flaking of photoresist material, the minimum value of Bshould be at least 1 mm. For the above example of a 200 mm semiconductorwafer, the diameter of photoresist layer 40 on the wafer (afterphotolithographical formation of edge 46) should not exceed 198 mm. Theminimum value of A then should be at least 1 mm+at least 0.5 mm for atotal of at least 1.5 mm, The maximum diameter of the ARC layer, in theabove example, would then be 197 mm.

The result is a photoresist layer-free and ARC layer-free peripheralupper surface 8 on substrate 2 bounded by a smooth and accurate sidewall46 on photoresist layer 40 due to the photolithographic termination ofthe outer perimeter of photoresist layer 40. Particle/flake formation,caused by engagement of this smooth outer surface 8 of substrate 2 withsubstrate handling apparatus, is thereby inhibited if not completelyeliminated by the process of the invention.

Having thus described the invention what is claimed is:
 1. A process forformation of a photoresist-free and antireflective coating (ARC)-freeperipheral upper surface portion of a semiconductor substrate adjacentthe end edge of said substrate by the steps of: a) forming an ARC layeron said upper surface portion of said semiconductor substrate; b)chemically treating said ARC layer to chemically terminate said ARClayer a first distance from the end edge of said substrate, leaving saidARC layer on said upper surface of said semiconductor substrate with achemically formed uneven end edge thereon; c) forming a photoresistlayer over said semiconductor substrate and over said ARC layer thereonto completely cover said chemically formed uneven end edge of said ARClayer; d) exposing said photoresist layer to a radiation pattern fromabove said photoresist layer which exposes only the peripheral portionof said photoresist layer larger than said chemically treated ARC layer,followed by; e) developing said exposed peripheral portion of saidphotoresist layer to remove said exposed peripheral portions of saidphotoresist layer, and thereby photolithographically terminating saidphotoresist layer a second distance from said end edge of said substratewherein said second distance from said end edge of said substrate issmaller than said first distance, from said end edge of said substrate;whereby said remaining photoresist layer still completely covers saidchemically formed uneven edge of said chemically terminated ARC layer.2. The process of claim 1 wherein said first distance is at least 1.5 mmfrom said end edge of said substrate.
 3. The process of claim 1 whereinsaid first distance is less than 3 mm from said end edge of saidsubstrate.
 4. The process of claim 2 wherein said second distance is atleast 1 mm from said end edge of said substrate.
 5. The process of claim1 wherein said second distance is no greater than at least 0.5 mm lessthan said first distance.
 6. The process of claim 1 wherein said firstdistance ranges from at least 1.5 mm to less than 3 mm.
 7. The processof claim 1 wherein said second distance ranges from at least 1 mm to nogreater than 0.5 mm less than said first distance.
 8. A process forformation of a photoresist-free and antireflective coating (ARC)-freeperipheral upper surface portion of a semiconductor substrate adjacentthe end edge of said substrate by the steps of: a) forming an ARC layeron one surface of said semiconductor substrate; b) chemically treatingsaid ARC layer with a solvent for said ARC layer to chemically terminatesaid ARC layer, and to chemically form an uneven end edge on said ARClayer a first distance of at least 1.5 mm from the end edge of saidsubstrate; c) forming a photoresist layer over said semiconductorsubstrate and completely over said ARC layer thereon to completely coversaid ARC coating and said chemically formed uneven end edge of sid ARClayer; d) exposing the peripheral portion of said photoresist layerlarger than said chemically formed uneven end edge of said ARC layer toa pattern of radiation; and then; e) developing said exposed peripheralportion of said photoresist layer to photolithographically terminatesaid photoresist layer a second distance of at least 1 mm from said endedge of said substrate wherein said second distance is smaller than saidfirst distance.
 9. The process of claim 8 wherein said first distance isless than 3 mm from said end edge of said substrate.
 10. The process ofclaim 8 wherein said second distance is no greater than at least 0.5 mmless than said first distance.
 11. A process for formation of aphotoresist-free and antireflective coating (ARC)-free peripheral uppersurface portion of a semiconductor substrate adjacent the end edge ofsaid substrate by the steps of: a) forming an ARC layer on one, surfaceof a semiconductor substrate; b) chemically treating said ARC layer witha solvent for said ARC layer to chemically terminate said ARC layer andto chemically form an uneven end edge on said ARC layer a first distanceof at least 1.5 mm but less than 3 mm from the end edge of saidsubstrate; c) forming a photoresist layer over said semiconductorsubstrate and over said ARC layer thereon; on to completely cover saidARC coating and said chemically formed uneven end edge of sid ARC layer;d) exposing the peripheral portion of said photoresist layer to apattern of radiation; and e) developing said exposed peripheral portionof said photoresist layer to photolithographically terminate saidphotoresist layer a second distance of at least 1 mm, but no greaterthan at least 0.5 mm less than said first distance, from said end edgeof said substrate wherein said second distance is smaller than saidfirst distance and said chemically formed uneven end edge of said ARClayer remains completely covered by said photoresist layer.
 12. Theprocess of claim 11 wherein said end edge of said substrate defines anypoint at the circular edge of said substrate at which a line at atangent with said circular edge of said substrate is perpendicular to aline lying in the plane of said substrate.